Yellow maple leaves

Asked October 7, 2019, 3:24 PM EDT

I have two large leaf maples and by mid August the leaves slowly started to turn yellow. What would cause this? I have attached photos. Thank you, Joe Riordan

Multnomah County Oregon tree health maple trees trees

1 Response

Thank you for choosing Ask an Expert for help with your maple tree.

I see how the focus can be on the yellowing leaves, but I am also seeing that the new growth—the leaves at the tips of the branches—is green and the leaves are a good size. This indicates to me that the tree is in somewhat good shape, in general.

The yellowing between the veins and the browning edges suggests that the tree is not getting the nutrients and water it needs. Why might this be?

I can see green grass in the area. It might be that this grass is taking up nutrients the tree needs. It is recommended that the root zone of a tree be clear of competing plants out to the drip line (the width of the leaf canopy), at least for a few years. This expands as the tree grows. A mulch of compost or bark chips can keep weeds down and moisture in the root zone.

Water is another factor. This season saw wide swings in temperatures during the early growing season. Many plants had difficulty getting enough water to the leaves as the thermometer shot up. After the past three years of drought conditions, a young tree might not have been able to develop an extensive enough root system as it would have otherwise.

Also, the tree’s root system extends to and past the drip line boundary. In the coming season, ensure that both fertilizer and water are distributed in this area, not just at the base of the trunk. Fertilizer can be applied in late summer/fall or in spring, as the leaves begin to expand. I would wait until spring, at this point. For more information on feeding your trees, check out this Oregon Extension publication Fertilizing Shade and Ornamental Trees here: https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/fs103.pdf

Regards,